The object of the present invention is to provide a process for manufacturing chemically resistant and thermally stable unsaturated polyester resins possessing a regular network structure.
A three-stage process for manufacturing unsaturated polyester resins has been described in U.S. Pat. No. 3,901,953. A dialkyl terephthalate is reacted with a polyhydric alcohol in the first stage, the reaction product being polycondensed in the second stage with an unsaturated dicarboxylic acid, a polyhydric alcohol or with a saturated dicarboxylic acid. In the third stage, the thus obtained unsaturated polyester is dissolved in a vinyl monomer to yield an unsaturated polyester resin. The first and second reaction steps are carried out in the presence of hydroquinone and a phosphite.
Polish Pat. No. 57016 (corresponding to DOS No. 1745 241) and No. 87109 disclose polyester manufacturing processes based on the simultaneous introduction of an unsaturated acid anhydride e.g. maleic anhydride, and a glycol, e.g. 1,2-propylene glycol, into the reacton medium in addition to a diene adduct of 2-naphthol and maleic anhydride, the molar ratio of the total acid components to glycols being equal to 1. Linear unsaturated polyesters obtained by the above methods feature a random arrangement of double bonds along the chain. Unsaturated polyester resins are obtained from the aforementioned polyesters by dissolving them in cross-linking monomers, e.g. styrene, which give, on cross-linking, cured polyester resins having a random, irregular network structure, which in turn results in a deterioration of their physical and mechanical properties and chemical resistance.
It is the object of the present invention to produce a cured polyester resin with improved physical, mechanical and chemical resistance properties.